Chronic diarrhea is a severe clinical disorder in AIDS patients, often contributing substantially to death. The etiology of this syndrome was assessed by extensive cultures and panendoscopy with biopsy. AIDS patients with diarrhea for more than two weeks are eligible for study. A complete microbiological evaluation of three stools is performed, followed by a malabsorption workup (fecal fat, D- Xylose absorbtion, Schlling test) and then upper endoscopy and lower endoscopy with biospsies. Any treatable process identified is treated. The significance of this work is the identification of factors that contribute to the morbidity and mortality of AIDS, particularly the inanition associated with AIDS, so that the currently dreadful prognosis of this underlying disease can be improved. A likely etiology of diarrhea has been found in over 50% of cases, including Kaposi's sarcoma, cytomegalovirus, giardia, ameba, and ayitosporida. Therapeutic approaches have been attempted with notable success in several cases of CMV colitis, a previously untreatable illness. Other patients have shown partial improvement following therapy.